1. Field of the Invention
The present invention relates to a fiber-reinforced resin molded article and a method of manufacturing the same, and more specifically to a lightweight resin molded article reinforced with glass fiber or like fibers, which has excellent rigidity, bending strength, impact strength, uniformity of strength, resistance to local stress and torsion, such as a fiber-reinforced resin molded article having a rib structure or a rib-like structure in the interior of the molded article. The present invention also relates to an efficient method for manufacturing the same.
2. Description of the Related Art
Conventionally, there has been known a fiber-reinforced resin molded article reinforced by addition of fibers such as glass fiber. Since the fiber-reinforced resin molded article is excellent in mechanical characteristics such as tensile strength and bending strength, and in heat resistance, it is widely used for automobile parts such as in-pane cores, bumper beams, door steps, roof-racks, rear quarter panels, and air cleaner cases, and for construction/civil engineering materials"" such as panels for external walls or partition walls, and cable troughs. In manufacture of these fiber-reinforced resin molded articles, there may be employed an injection molding method for injecting a fiber-containing molten resin into a cavity within molds. This injection molding method enables molding of an article having an intricate shape, as well as mass production of articles of the same shape since a predetermined molding cycle can be repeated continuously.
When the amount of the fiber added to the fiber-reinforced resin molded article manufactured through injection molding is increased in order to improve the strength and rigidity thereof, the article tends to gain weight and suffer severe warp. For the purpose of reducing the weight of the molded articles, as well as solving other problems, Japanese Patent Application Laid-Open (kokai) Nos. 7-247679, etc. disclose an expansion injection molding method in which a foaming agent is added to resin material and the material is foamed and molded into a molded article. However, in this expansion injection molding method, if a considerable amount of foaming agent is used for reducing the weight of the molded article, a sufficient expansion ratio is not easily obtained. Even if a sufficient expansion ratio is obtained, the appearance of the molded article is impaired due to foaming, large pores are easily formed within the molded article, and uniform pores are not easily formed therein. Therefore, mechanical requirements such as strength, rigidity, and impact resistance may not be sufficiently met, despite the molded article containing fiber for reinforcement.
To solve the above-mentioned problems, and to reduce the weight of molded articles while maintaining the quality of appearance and mechanical characteristics such as strength, rigidity, and impact resistance of the molded article, the following techniques have been proposed: (1) an expansion molding method in which fiber-reinforced resin pellets containing relatively long fiber are melted into molten resin and the molten resin is expanded during molding through utilization of the springback phenomenon caused by the contained fiber, to thereby obtain a lightweight molded article; (2) an expansion molding method in which a foaming agent for supplementing the expansion of resin is mixed into the fiber-reinforced resin pellets in item (1) above in order to further reduce the weight of molded articles (International Patent Publication WO97/29896). These methods sufficiently reduce the weight of molded articles without impairing the mechanical characteristics thereof, and are effective in reduction of the weight of fiber-reinforced resin molded articles.
As another method, there has been proposed (3) a method of manufacturing foamed resin molded articles in which a molten resin containing a chemical foaming agent is charged, through injection or injection compression, into the cavity of molds which comprise a movable core having a slit; the resin surface in contact with the mold is cooled and solidified without foaming; the capacity of the cavity is expanded by moving the movable core so as cause the molten resin to foam in the increased capacity of the cavity, to thereby manufacture a foamed resin molded article having a rib structure (Japanese Patent Application Laid-Open (kokai) No. 9-104043).
However, depending on the degree of weight reduction (expansion) or shape of a molded article; for example, in such a case in which the molded article has a large region or capacity the molded article obtained through the above method (1) or (2) may have insufficient bending strength and rigidity, yet insufficient resistance to local stress, low uniformity of strength and resistance to torsion, requiring improvements. In the above method (3) using a foaming agent, expansion of the foaming agent is difficult to suppress at the time of injection. Especially, during injection molding with compressed pressure, the resin tends to foam at the time of injection due to reduction in resin pressure, resulting in silver marks on the surface of the resultant molded article. Also, at a high expansion ratio, large pores are formed within the foamed portion as shown in the Examples herein, resulting in a molded article of poor uniformity. Moreover, even if reduction of the weight is achieved, molded articles having sufficient strength are not easily obtained. Furthermore, since the foamed product comes to have closed cells, the cooling time of the resultant molded article is extended. As a result, the molding cycle is prolonged, which is a problem in productivity.
An object of the present invention is to provide a fiber-reinforced resin molded article which has excellent bending strength, rigidity, impact strength, heat resistance, sufficient resistance to local stress and torsion, and uniformity.
Another object of the present invention is to provide a method of manufacturing such a resin molded article.
In view of the foregoing, the present inventors conducted careful studies on the overall structurexe2x80x94including the internal structurexe2x80x94of fiber-reinforced lightweight resin molded articles with dispersed pores therein and the properties thereof. As a result, they found that, in a conventional method in which a movable core is simply retracted for expansion, there is obtained a resin molded article having a non-expansion or low-expansion portion formed in the peripheral edge thereof, and near-uniform expansion occurs in other general portions such as the central portion thereof having a flat-shaped structure. They also found that if a molded article has a coarse-and-dense structure in terms of pores rather than the case in which pores are uniformly dispersed over the entirety of a molded article, and the molded article also has a unique rib-like structure by which a function of a rib is exerted between the two skin layers, the properties of the molded article are improved.
In connection with the method of forming the above-mentioned rib or rib-like structure within a resin molded article, the present inventors found firstly that if a grooved portion is provided in the thickness direction of a uniformly expanded portion, the grooved portion serves as a structure equivalent to a rib having a low porosity. They also found that the structure is attained through a method in which fiber-containing molten thermoplastic resin is injected into a cavity formed by a movable core which can advance and retract relative to the cavity of the mold and which has a protruding portion for forming a grooved portion of the molded article, and in which the movable core is subsequently retracted so as to expand the capacity of the cavity.
Secondly, they found that if a low- or non-expansion portion is formed through changing the degree of expansion relative to the uniformly expanded portion of the molded article having a substantially uniform thickness, the low- or non-expansion region advantageously comes to substantially serve as a rib structure. They also found that the molded article having this structure can be manufactured through a molding method in which only the regions corresponding to the movable portions are expanded by use of a movable core which can advance and retract relative to the cavity and which has a plurality of cavity molding surfaces (movable core having a plurality of movable portions).
Thirdly, the present inventors found that the properties of a molded article are improved if the structure of a uniformly expanded portion is changed so that the molded article attains a kind of rib structure in which substantially no or very few pores are formed in the thickness direction between the skin layers, and that such a molded article can be manufactured through provision of a slit on the cavity side of the movable core.
Fourthly, the present inventors found that if a rib-like or dispersing-type protruding portion is formed on a uniformly expanded portion, the protruding portion exhibits reinforcement effects similar to those of a rib, and, in addition, that if a fiber-containing molten resin (thermoplastic resin) is expanded, the region corresponding to the protruding portion, i.e., the portion of the protruding portion plus the region of the body thereunder, obtains a low-expanded, i.e., low-porosity dense structure as compared to other flat portions. They also found that the molded article having this structure can be manufactured through a method in which fiber-containing molten resin is injected into a specific mold cavity, and one mold is retracted toward the direction in which the mold cavity is expanded.
Based on the above findings, the present inventors have accomplished the present invention. Accordingly, the present invention provides the following:
(1) A fiber-reinforced lightweight resin molded article having pores, which comprises in the molded article a portion having a porosity lower than that of other general portions.
(2) The fiber-reinforced lightweight resin molded article according to item (1) above, wherein the portion having a porosity lower than that of other general portions is formed in the thickness direction of the molded article.
(3) The fiber-reinforced lightweight resin molded article according to item (1) above, wherein the portion having a porosity lower than that of other general portions has a rib structure or a rib-like structure.
(4) A fiber-reinforced lightweight resin molded article having pores, wherein a grooved portion is formed in the thickness direction of the molded article.
(5) A fiber-reinforced lightweight resin molded article according to item (4) above, wherein a resin portion forming a grooved portion has a porosity lower than that of other flat portions.
(6) A fiber-reinforced lightweight resin molded article according to item (4) or (5) above, wherein the molded article contains 10-70 wt. % glass fiber having a mean fiber length of 1-20 mm.
(7) A fiber-reinforced lightweight resin molded article according to any of items (4)-(6) above, wherein a face material is integrally molded with the molded article.
(8) A method of manufacturing a fiber-reinforced lightweight resin molded article having a grooved portion in the thickness direction of the molded article, which comprises the steps of injecting a fiber-containing molten thermoplastic resin into a mold cavity formed within a mold having a movable core which can advance and retract relative to the mold cavity and also having a protruding portion for forming a grooved portion in the molded article in the thickness direction of the molded article; and retracting the movable core toward the direction in which the capacity of the mold cavity is expanded.
(9) A method of manufacturing a fiber-reinforced lightweight resin molded article according to item (8) above, wherein a fiber-containing molten thermoplastic resin is injected into a mold cavity formed by a fixed mold, a moving mold having a protruding portion for forming a grooved portion of the molded article, and a movable core capable of advancing and retracting within the moving mold.
(10) A method of manufacturing a fiber-reinforced lightweight resin molded article according to item (9) above, wherein at the time of injection a part of a mold cavity is defined by a gap between the protruding portion of a moving mold and a movable core.
(11) A method of manufacturing a fiber-reinforced lightweight resin molded article according to any of items (8)-(10) above, wherein a gas is injected into the interior of the fiber-reinforced lightweight resin molded article within the mold cavity.
(12) A method of manufacturing a fiber-reinforced lightweight resin molded article according to any of items (8)-(11) above, wherein a fiber-containing molten thermoplastic resin is injected into the mold cavity on the surface of which a face material is applied in advance.
(13) A method of manufacturing a fiber-reinforced lightweight resin molded article according to any of items (8)-(12) above, wherein the fiber-containing molten thermoplastic resin is obtained by plasticizing and melting fiber-containing thermoplastic resin pellets having a length of 2-100 mm and contains parallel-arranged fiber having the same length in an amount of 20-80 wt. % with respect to the weight of the resultant resin-fiber mixture, or obtained by plasticizing and melting a mixture of the pellets and other pellets containing fiber so that the amount of fibers is 10-70 wt. % with respect to the weight of the entirety of the mixture.
(14) A fiber-reinforced lightweight resin molded article containing pores, wherein portions other than the peripheral portion of the molded article are composed of a plurality of regions having different expansion coefficients.
(15) A fiber-reinforced lightweight resin molded article according to item (14) above, wherein portions other than the peripheral portion of the molded article are composed of a low expansion coefficient region having an expansion coefficient of 1.0-1.5 and a high expansion coefficient region having an expansion coefficient of 1.6-8.
(16) A fiber-reinforced lightweight resin molded article according to item (14) or (15) above, wherein the fiber contained in the molded article is glass fiber having a mean fiber length of 1-20 mm and the content thereof is 10-70 wt. %.
(17) A fiber-reinforced lightweight resin molded article according to any of items (14)-(16) above, wherein a face material is integrally molded with the molded article.
(18) A method of manufacturing a fiber-reinforced lightweight resin molded article, wherein a fiber-containing molten thermoplastic resin is injected into a cavity corresponding to a clearance provided by a movable core which has a plurality of surfaces facing the cavity and which can advance and retract relative to the mold cavity, and then the movable core is retracted toward the direction in which the capacity of the mold cavity is expanded.
(19) A method of manufacturing a fiber-reinforced lightweight resin molded article according to item (18) above, wherein a gas is injected into the interior of the fiber-containing molten thermoplastic resin in the mold cavity.
(20) A method of manufacturing a fiber-reinforced lightweight resin molded article according to item (18) or (19) above, wherein a fiber-containing molten thermoplastic resin is injected into the mold cavity on the surface of which a face material is applied in advance.
(21) A method of manufacturing a fiber-reinforced lightweight resin molded article according to any of items (18)-(20) above, wherein the fiber-containing molten thermoplastic resin is obtained by plasticizing and melting fiber-containing thermoplastic resin pellets having a length of 2-100 mm and contains parallel-arranged fiber having the same length in an amount of 20-80 wt. % with respect to the weight of the resultant resin-fiber mixture, or obtained by plasticizing and melting a mixture of the pellets and other pellets containing fiber so that the amount of fibers is 10-70 wt. % with respect to the weight of the entirety of the mixture.
(22) A fiber-reinforced resin molded article comprising skin layers, a fiber-containing coarse region having substantially continuous pores, and a fiber-containing dense region having substantially no continuous pores, wherein the dense region constitutes a rib structure which bridges the skin layers.
(23) A fiber-reinforced resin molded article according to item (22) above, wherein the fiber-containing coarse region has a porosity of 50-90% and the fiber-containing dense region has a porosity of 0-30%.
(24) A fiber-reinforced resin molded article according to item (22) or (23) above, wherein the fiber contained in the molded article is glass fiber having a mean fiber length of 1-20 mm and the content thereof is 10-70 wt. %.
(25) A fiber-reinforced resin molded article according to any of items (22)-(23) above, wherein a face material is integrally molded with the molded article.
(26) A method of manufacturing a fiber-reinforced resin molded article comprising a rib structure, wherein a fiber-containing molten resin is injected or compression-injected into a cavity formed by molds including a movable core which has a slit in communication with the cavity, and then the movable core is retracted toward the direction in which the capacity of the mold cavity is expanded.
(27) A method of manufacturing a fiber-reinforced resin molded article according to item (26) above, wherein the cavity is formed by a fixed mold, a moving mold, and a movable core which can advance and retract within the moving mold relative to the mold cavity.
(28) A method of manufacturing a fiber-reinforced resin molded article according to item (26) or (27) above, wherein a gas is injected into the interior of the fiber-containing molten resin in the cavity after the start of retracting of the movable core.
(29) A method of manufacturing a fiber-reinforced resin molded article according to any of items (26)-(28) above, wherein a fiber-containing molten resin is injected or compression injected into the cavity, on the surface of which a face material is applied in advance.
(30) A method of manufacturing a fiber-reinforced resin molded article according to any of items (26)-(29) above, wherein the fiber-containing molten thermoplastic resin is obtained by plasticizing and melting fiber-containing thermoplastic resin pellets having a length of 2-100 mm and contains parallel-arranged fiber having the same length in an amount of 20-80 wt. % with respect to the weight of the resultant resin-fiber mixture, or obtained by plasticizing and melting a mixture of the pellets and other pellets containing fiber so that the amount of fibers is 10-70 wt. % with respect to the weight of the entirety of the mixture.
(31) A fiber-reinforced lightweight resin molded article comprising a protruding portion, wherein the molded article contains pores and has a protruding portion on at least one of the surfaces extending perpendicularly to the thickness direction of the molded article, and the porosity of the region corresponding to the protruding portion is lower than that of other flat portions.
(32) A fiber-reinforced lightweight resin molded article comprising a protruding portion according to item (31) above, wherein the porosity of the region corresponding to the protruding portion is 0.1-60% and that of other flat portions is 30-90%.
(33) A fiber-reinforced lightweight resin molded article according to item (31) or (32) above, wherein the fiber contained in the molded article is glass fiber having a mean fiber length of 1-20 mm and the content thereof is 10-70 wt. %.
(34) A fiber-reinforced lightweight resin molded article according to any of items (31)-(33) above, wherein a face material is integrally molded with the molded article.
(35) A method of manufacturing a fiber-reinforced lightweight resin molded article comprising a protruding portion, wherein a fiber-containing molten resin is injected into a cavity formed by a pair of molds, one of which has a grooved portion for forming a protruding portion, and then one of the molds is retracted toward the direction in which the capacity of the mold cavity is expanded, whereby the porosity of the region corresponding to the protruding portion is lower than that of other flat portions.
(36) A method of manufacturing a fiber-reinforced lightweight resin molded article comprising a protruding portion according to item (35) above, wherein a gas is injected into the interior of the fiber-containing molten resin in the cavity.
(37) A method of manufacturing a fiber-reinforced lightweight resin molded article according to item (35) or (36) above, wherein a fiber-containing molten resin is injected into the cavity on the surface of which a face material is applied in advance.
(38) A method of manufacturing a fiber-reinforced lightweight resin molded article comprising a protruding portion according to any of items (35)-(37) above, wherein the fiber-containing molten thermoplastic resin is obtained by plasticizing and melting fiber-containing thermoplastic resin pellets having a length of 2-100 mm and contains parallel-arranged fiber having the same length in an amount of 20-80 wt. % with respect to the weight of the resultant resin-fiber mixture, or obtained by plasticizing and melting a mixture of the pellets and other pellets containing fiber so that the amount of fibers is 10-70 wt. % with respect to the weight of the entirety of the mixture.
According to the present invention, there is provided a fiber-reinforced resin molded article which has excellent bending strength, rigidity, impact resistance, heat resistance, sufficient resistance to local stress and torsion, and uniformity. Also, in the method of manufacturing the same according to the present invention, reduction in the weight of a molded article can be arbitrarily regulated by use of molds having relatively simple structure, and the excellent surface quality of a molded article can be obtained, for example, the flat structure of the exterior of a highly lightweight molded article can be maintained.